A stable single-atom Zn catalyst synthesized by a ligand-stabilized pyrolysis strategy for selective oxidation of C–H bonds

Abstract

The activation of C–H bonds for the synthesis of highly valued chemicals is still a challenging task. Herein, a nitrogen-doped carbon supported single atom Zn catalyst (Zn–N–C) was fabricated via a ligand-stabilized pyrolysis strategy, in which 2,2′-bipyridine (bipy) served as a ligand and graphitic carbon nitride (g-C₃N₄) served as a directional 2D-template and a nitrogen source. The results of high-angle annular dark field aberration corrected scanning transmission electron microscopy (HAADF-STEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy indicated that Zn species are present as isolated single sites and stabilized by nitrogen in the Zn–N₄ structure. The optimized Zn–N–C-900 catalyst displayed superior catalytic performance for the selective oxidation of C–H bonds. In particular, the Zn–N–C-900 catalyst can be reused fifteen times without obvious decay in either activity or selectivity. Density functional theory calculations were conducted to reveal the reaction mechanism. The results indicated that the high valence ZnO species generated on Zn–N–C-900 were the crucial active centers for the activation of C–H bonds.